1. Field of the Invention
This invention relates generally to a fuel fired apparatus for cooking food and, more particularly, to a griddle system for use in commercial food services.
2. Description of Prior Art
Griddles are major cooking appliances in commercial kitchens, particularly fast food and full-service chain restaurants. Typically, such griddles consist of a large flat steel plate which is heated from below by a heating element, either fuel fired or electric, and typically employ one heating element, one thermocouple and one thermostat per linear foot which results in wide temperature variations between heating elements. The plate size usually ranges from two feet deep by two to six feet long by 3/4 to one inch in thickness. The massive steel plate (griddle plate) and heating system have evolved such that the griddle plate creates a hard flat surface for cooking as well as storing a significant amount of heat that can be transferred to the food product during the initial phase of cooking, and the burner or heating system provides sufficient heat to the griddle to recover temperature during the cooking cycle.
Although in use for many years, conventional griddle designs have many disadvantages including poor plate temperature distribution due to low thermal conductivity of the steel plate. Such griddles typically have a 70.degree. F. temperature variation across their surfaces and are unable to deliver heat to specific incremental areas. As a result, applying heat to cold areas further overheats hot areas, or vice-versa. In addition, due to the large mass of the plate, heat-up time from the point of turn-on is lengthy and response time of the plate to a cooking load is poor. Finally, recovery time of the plate between cooking loads or when the food product is turned over is also poor.
For the equipment operator, conventional griddle designs give rise to a number of issues including cooking safety due to non-uniform cooking surface temperatures, reduced cooking capacity due to the fact that a large border (about a three-inch strip) area is not at cooking temperature, reduced cooking capacity due to the time lag to diffuse the heat through the plate after a load is cooked and after a food product is turned from top to bottom, high operating costs due to the long idle periods and low capacity, low efficiency due to the heating element/plate design, and increased floor space due to low griddle surface capacity.
Several companies have introduced newer griddle products that address some of these issues. Griddles with infrared gas combustion systems are beneficial in promoting uniform temperature across the entire area of the griddle plate. U.S. Pat. No. 5,227,597 to Dickens et al. teaches a griddle employing magnetically permeable, tri-clad griddle plates heated by induction coils to their Curie temperature resulting in griddle plates which are quickly heated to a uniform, essentially constant temperature across their surfaces. See also U.S. Pat. No. 5,134,265 to Dickens et al.
In an attempt to address some of these issues, griddle plates in which the stainless steel plate is mechanically, for example, bolted, connected to a thick aluminum plate have been developed. The mechanical clad design helps in temperature uniformity, but it suffers from a thermal standpoint given the contact resistance between the plates, and it still retains significant response issues associated with the large thick aluminum plate. In addition, the manufacturing of such composite plates with numerous bolted connections is time consuming. U.S. Pat. No. 5,413,032 to Bruno et al. teaches a multi-zone griddle which is modularly constructed and load sensitive which includes a steel griddle plate 3/8" thick with upper and lower surfaces that are ground flat and, in intimate contact with the lower surface thereof, a heat spreader in the form of an aluminum plate which is about 1/8" thick. Aluminum is selected because it is soft relative to the hardness of the steel griddle plate and is given to cold flow so that soon after it is installed, the upper aluminum surface adopts to the shape of the bottom of the steel griddle plate, filling in surface valleys and giving way to surface hills.
U.S. Pat. No. 5,676,043 teaches a griddle plate made of a thin, relatively low conductivity metal and received along its bottom surface substantially thick, juxtaposed heat transfer blocks disposed in spaced relationship, side-by-side, beneath and laminated to discrete portions of the griddle plate. The upper relatively low conductivity metal plate is stainless steel and the lower discrete blocks or plates are aluminum. The plates are bonded together with a thin silicone material which is said to improve the heat distribution within the lower block because the bond causes a small resistance to the heat flow and forces the improved distribution of the energy. One of the problems associated with mechanical attachment between the stainless steel griddle plate and the lower aluminum plate is that mechanical attachment does not insure integral contact between the two plates due to oxidation or breakdown of the thermal bonding material which can form between the plates and local warping which causes small gaps to occur between the plates.
In addition to providing a good cooking surface relative to thermal distribution, a griddle plate must stay flat. Due to the use of dissimilar materials in multi-layered griddle plates, thermal distortion, that is, bending resulting from different coefficients of thermal expansion of the different material layers, can be a problem.